Methods and systems for converting volatile fatty acids to lipids

ABSTRACT

Methods and systems for simultaneously enhancing the production of both methane and volatile fatty acids in an anaerobic digestion bioreactor are disclosed. In some embodiments, the methods include: providing a stream of organic feedstock; providing a plurality of anaerobic digester bioreactors, each of the plurality of anaerobic digester bioreactors connected in series; step-feeding predetermined percentages of the stream of organic feedstock to two or more of the plurality of anaerobic digester bioreactors; feeding effluent from each of the plurality of anaerobic digester bioreactors to a subsequent one of the plurality of anaerobic digester bioreactors; and anaerobically digesting at least one of the stream of organic feedstock and the effluent from each of the plurality of anaerobic digester bioreactors to develop a final effluent stream including methane and volatile fatty acids. The volatile fatty acids are then microbially converted to lipids in an aerobic bioreactor.

CROSS REFERENCE TO RELATED APPLICATION(S)

This application is a continuation of U.S. patent application Ser. No.14/567,271, filed Dec. 11, 2014, which claims the benefit of U.S.Provisional Application Nos. 61/915,788, filed Dec. 13, 2013, and62/090,102, filed Dec. 10, 2014, each of which is incorporated byreference as if disclosed herein in its entirety.

BACKGROUND

In developing countries, 2.6 billion people remain without access to anykind of sanitation and 850 million remain undernourished. Thus, there isa critical need to develop sustainable technologies that providesanitation while simultaneously recovering valuable nutrients andresources from the waste. Biofuels have not found widespread applicationso far because of higher cost and the significant stress they exert uponthe agricultural commodities.

Biocatalysis of organic waste into useful chemical feedstock is apromising approach for managing waste and providing a renewable energysupply such as diesel. However, many current methods for producingrenewable energy sources suffer from low yields and/or production fromfood commodities resulting in competition for crop resources.

Most lipids for commercial biodiesel production today are derived fromfood and agricultural commodities, e.g. soybean, jatropha oil, etc.,inadvertently contributing to the rising food prices. Therefore, it ispreferred to produce non-edible sources of lipids, in particular, lipidsderived from oleaginous microorganisms such as yeast and other fungi,which have the capability to assimilate inexpensive organic carbonsources produced from existing technologies such as anaerobicfermentation and digestion and store them as lipids.

Anaerobic digestion has been practiced for centuries, but is stillplagued by limitations to adequate mixing in the anaerobic bioreactors.Additionally, using bioreactor designs and operating configurationsdeveloped to date, it is only possible to either maximize methaneproduction or volatile fatty acids. This results in high operating andcapital costs for a given methane or acid output.

Organic material from waste water, sewage, and industrial waste can bereused to produce biogas using anaerobic digestion. Biogas, such asmethane and volatile fatty acids, can be used for energy and as buildingblocks for chemical production, respectively. In anaerobic digestion,the organic material, or feedstock, is dissolved in water and mixed withmethane and acid producing bacteria. However, current anaerobicdigestion bioreactors suffer from lower yields of biogas production dueto limited mixing between the feedstock and bacteria. In addition, thedesign of these bioreactors also allows for maximizing the yields ofeither methane or volatile fatty acids only, but not both.

SUMMARY

Methods and systems according to the disclosed subject matter includeanaerobic bioreactors using a step feed pattern to simultaneouslyincrease the yield of methane and volatile fatty acid production. A stepfeed pattern introduces the feedstock to the bioreactor during differentstages of digestion, rather than all the material at once in thebeginning. This step feed pattern allows better mixing of the feedstockwith the microbes, increasing the yield and kinetics of both methane andvolatile fatty acid production in computer simulations. In addition, thestep feed design allows the bioreactor to consist of multiple smallertanks that may be better suited for environments with less availablespace.

Some embodiments of the disclosed subject matter include an aerobicbiological process, wherein the volatile fatty acids produced fromanaerobic fermentation of various substrates, are converted into lipids.In some embodiments, the biocatalysts used include yeast and fungi,which are cultivated in aerated reactors and fed with volatile fattyacids. By optimizing process operating conditions including pH,hydraulic retention time, initial or influent volatile fatty acidconcentration and the relative organic carbon to nitrogen ratio in thefeed, the lipid content of the biocatalysts is maximized.

Some embodiments of the disclosed subject matter include a method toproduce lipids using substrates, i.e., volatile fatty acids, which arewidely produced during anaerobic digestion of organic wastes andsubstrates. Lipids are an attractive product, since they can beconverted directly to biodiesel. It is possible to convert just aboutany organic compound (through first anaerobic conversion to volatilefatty acids) to lipids. Systems according the disclosed subject matterare superior to current lipid pipelines for biodiesel, including algae,since the yeasts and fungi used herein can convert volatile fatty acidsto lipids, which algae cannot.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings show embodiments of the disclosed subject matter for thepurpose of illustrating the invention. However, it should be understoodthat the present application is not limited to the precise arrangementsand instrumentalities shown in the drawings, wherein:

FIG. 1 is a schematic diagram of methods and systems according to someembodiments of the disclosed subject matter; and

FIG. 2 is a chart of a method according to some embodiments of thedisclosed subject matter.

DETAILED DESCRIPTION

Referring again to FIGS. 1 and 2, aspects of the disclosed subjectmatter include methods and systems using bioreactors for enhancing theproduction of both methane and volatile fatty acids and converting thevolatile fatty acids to lipids.

Referring now to FIG. 1, some embodiments include a system 100 forconverting volatile fatty acids 102 to lipids 104 using a feedstocktreatment module 106 to produce both methane 108 and volatile fattyacids 110 and an aerobic bioreactor 112 for converting the volatilefatty acids to lipids.

System 100 includes a supply stream of organic feedstock 114 that istypically stored in a tank 116 and pumped to feedstock treatment module106. Methods and systems according to the disclosed subject matter areadaptable for simultaneously enhancing the production of methane andvolatile fatty acids from virtually any organic feedstock, including butnot limited to the following: Wastewater; Sewage sludge; Fecal sludge;Agricultural waste; Animal processing waste; Municipal solid organicwaste; Food waste; and Industrial waste, including but not limited tobrewery waste, pharmaceutical waste, biodiesel waste, chemical waste.

Feedstock treatment module 106 is used to enhance the production of bothmethane and volatile fatty acids from supply stream of organic feedstock114. Feedstock treatment module 106 includes a plurality of anaerobicdigester bioreactors, e.g., in some embodiments as shown in FIG. 1,there are six bioreactors, AD1-AD6, that are fluidly connected in seriesand fluidly joined with supply stream of organic feedstock 114. Aplurality of adjustable diverter valves (VI-V3) are used forstep-feeding predetermined percentages of supply stream of organicfeedstock 114 to two or more, e.g., in some embodiments, as shown inFIG. 1, four bioreactors, AD1, AD2, AD4, and AD6, of plurality ofanaerobic digester bioreactors (AD1-AD6). In some, but not allembodiments, system 100 includes a feedstock pretreatment filter 118 forsterilizing volatile fatty acids 102 included in supply stream oforganic feedstock 114 before they are fed to plurality of anaerobicdigester bioreactors (AD1-AD6). In some embodiments, e.g., wherefeedstock 114 is pre-fermented with high concentrations of volatilefatty acids, feedstock pretreatment filter 118 is placed after the finalbioreactor, i.e., AD6 in FIG. 1, and the volatile fatty acids aresterilized prior to feeding them to aerobic bioreactor 112. After supplystream of organic feedstock 114 passes through anaerobic digesterbioreactors AD1-AD6, a final effluent stream 120, which includesenhanced amounts of methane 108 and volatile fatty acids 110, exits thelast one of the bioreactors in the series, i.e., AD6 in FIG. 2. In someembodiments, a substantial amount of the methane present and produced iscollected from one or more of anaerobic digester bioreactors AD1-AD6 andonly a nominal amount of methane 108 is present in final effluent stream120.

In some embodiments, one of the plurality of anaerobic digesterbioreactors, e.g., AD1, is step-fed about 50 to about 80 percent ofsupply stream of organic feedstock 114 and three of the plurality ofanaerobic digester bioreactors, e.g., AD2, AD4, and AD6, are eachstep-fed about 5 to about 15 percent of the supply stream of organicfeedstock. In some embodiments, one of the plurality of anaerobicdigester bioreactors, e.g., AD1, is step-fed about 70 percent of supplystream of organic feedstock 114 and three of the plurality of anaerobicdigester bioreactors, e.g., AD2, AD4, and AD6, are each step-fed about10 percent of the supply stream of organic feedstock. As one skilled inthe art will appreciate, the particular flow split percentages of supplystream of organic feedstock 114 that are sent to particular ones of thebioreactors varies depending on the characteristics of the feedstock.

In some embodiments, final effluent stream 120 exits feedstock treatmentmodule 106 and enters aerobic bioreactor 112 where volatile fatty acids110 are microbially converted to lipids 104. Typically, but not always,microorganisms including Cryptococcus albidus yeast or Fusariumoxysporum fungus microbially converts volatile fatty acids in finaleffluent stream 120 to lipids 104.

In some embodiments, control module 124 includes a plurality of monitors(not shown), e.g., wired or wireless, and a plurality of remotelyactuated valves (also not shown), which automatically monitor and adjustoperating conditions in plurality of anaerobic digester bioreactors(AD1-AD6) and aerobic bioreactor 112 by controlling diverter valvesVI-V3 and other valves not shown, by controlling one or more pumps (notshown) to adjust the flow, by controlling appropriate equipment (alsonot shown) to adjust temperatures in the bioreactors, by causingnitrogen or compounds including nitrogen to be added to one or more ofthe bioreactors to adjust the initial nitrogen concentration in aerobicbioreactor 112, and causing acidic or basic chemicals to be added to thebioreactors to adjust the pH. For example, in some embodiments, thetemperature in each of the plurality of anaerobic digester bioreactorsis maintained at about 20 to about 40 degrees Celsius, the pH in each ofthe plurality of anaerobic digester bioreactors is maintained at about5.5 to about 7.0, and an initial nitrogen concentration in finaleffluent stream 120 is about 4 to about 10 percent of an initialvolatile fatty acid concentration 102 in supply stream of organicfeedstock 114.

Referring now to FIG. 2, some embodiments include a method 200 forsimultaneously enhancing the production of both methane and volatilefatty acids in an anaerobic digestion bioreactor. At 202, a stream oforganic feedstock is provided. At 204, a first percentage of the streamof organic feedstock is split from the stream thereby developing a firstsplit stream of organic feedstock. In some embodiments, the firstpercentage is about 50 to about 80 percent of the stream of organicfeedstock. In some embodiments, the first percentage is about 70 percentof the stream of organic feedstock. At 206, the first split stream oforganic feedstock is fed to a first anaerobic digester bioreactor. At208, the first split stream of organic feedstock is anaerobicallydigested in the first anaerobic digester bioreactor thereby producing afirst anaerobic digester bioreactor effluent including methane andvolatile fatty acids. At 210, a second percentage of the stream oforganic feedstock is split from the stream thereby developing a secondsplit stream of organic feedstock. In some embodiments, the secondpercentage is about 5 to about 15 percent of the stream of organicfeedstock. In some embodiments, the second percentage is about 10percent of the stream of organic feedstock. At 212, the second splitstream of organic feedstock is fed to a second anaerobic digesterbioreactor. At 214, the first anaerobic digester bioreactor effluent isfed to the second anaerobic digester bioreactor. At 216, the secondsplit stream of organic feedstock and the first anaerobic digesterbioreactor effluent are anaerobically digested in the second anaerobicdigester bioreactor thereby producing a second anaerobic digesterbioreactor effluent including methane and volatile fatty acids. At 218,the second anaerobic digester bioreactor effluent is fed to a thirdanaerobic digester bioreactor. At 220, the second anaerobic digesterbioreactor effluent is anaerobically digested in the third anaerobicdigester bioreactor thereby producing a third anaerobic digesterbioreactor effluent including methane and volatile fatty acids. At 222,a third percentage of the stream of organic feedstock is split from thestream thereby developing a third split stream of organic feedstock. Insome embodiments, the third percentage is about 5 to about 15 percent ofthe stream of organic feedstock. In some embodiments, the thirdpercentage is about 10 percent of the stream of organic feedstock. At224, the third split stream of organic feedstock is fed to a fourthanaerobic digester bioreactor. At 226, the third split stream of organicfeedstock and the third anaerobic digester bioreactor effluent areanaerobically digested in the fourth anaerobic digester bioreactorthereby producing a fourth anaerobic digester bioreactor effluentincluding methane and volatile fatty acids. At 228, the fourth anaerobicdigester bioreactor effluent is fed to a fifth anaerobic digesterbioreactor. At 230, the fourth anaerobic digester bioreactor effluent isanaerobically digested in the fifth anaerobic digester bioreactorthereby producing a fifth anaerobic digester bioreactor effluentincluding methane and volatile fatty acids. At 232, a remainingpercentage of the stream of organic feedstock is fed to a sixthanaerobic digester bioreactor. In some embodiments, the remainingpercentage is about 5 to about 15 percent of the stream of organicfeedstock. In some embodiments, the remaining percentage is about 10percent of the stream of organic feedstock. At 234, the fifth anaerobicdigester bioreactor effluent is fed to the sixth anaerobic digesterbioreactor. At 236, the remaining percentage of the stream of organicfeedstock and the fifth anaerobic digester bioreactor effluent areanaerobically digested in the sixth anaerobic digester bioreactorthereby producing a final anaerobic digester bioreactor effluentincluding methane and volatile fatty acids. At 238, the final anaerobicdigester bioreactor effluent is fed to an aerobic bioreactor and thevolatile fatty acids are microbially converted to lipids.

Methods and systems according to the disclosed subject matter provide adistinct commercial and technological advantage overall existinganaerobic bioreactor designs in that it maximizes the production of bothmethane and volatile fatty acids by employing a novel step-feedstrategy. The step-feed strategy additional provides enhanced mixing ofthe feedstock in the bioreactor, thereby increasing process kinetics andefficiency even further, without the need for cost and energy intensiveexternal mixing devices. Methods and systems according to the disclosedsubject matter are adaptable for simultaneously enhancing the productionof methane and volatile fatty acids from virtually any organicfeedstock.

Methods and systems according to the disclosed subject matter employspecific step-feeding conditions for the anaerobic digestion process,which simultaneously maximize methane and volatile fatty acid yields andin addition enhance reactor mixing. Step-feeding to anaerobic digestersis unique.

The main advantages of methods and systems according to the disclosedsubject matter are as follows: 1. Simultaneous maximization of methaneand volatile fatty acid concentrations; and 2. Enhanced anaerobicreactor mixing.

Methods and systems according to the disclosed subject matter areadaptable for simultaneously enhancing the production of methane andvolatile fatty acids from virtually any organic feedstock and can alsobe applied to waste streams from existing domestic (including, but notlimited to high-rise multi-dwelling communities, new residential orcommercial developments, hospital or educational complexes).

Methods and systems according to the disclosed subject matter are anovel way to produce lipids using substrates (volatile fatty acids),which are widely produced during anaerobic digestion of organic wastesand substrates. Using methods and systems according to the disclosedsubject, it is possible to convert the volatile fatty acids into lipids.Lipids are an attractive product, since they can be converted directlyto biodiesel. Therefore, it is possible to convert just about anyorganic compound (through first anaerobic conversion to volatile fattyacids) to lipids. This system is also superior to current lipidpipelines for biodiesel, including algae, since the yeasts and fungiused herein can convert volatile fatty acids to lipids, which algaecannot. Additionally, this technology avoids the use of food commoditiesfor the production of biodiesel, including from jatropha or cookingoils. Instead, it provides a flexible platform for integrating wastetreatment into biofuels (biodiesel) production.

Although the disclosed subject matter has been described and illustratedwith respect to embodiments thereof, it should be understood by thoseskilled in the art that features of the disclosed embodiments can becombined, rearranged, etc., to produce additional embodiments within thescope of the invention, and that various other changes, omissions, andadditions may be made therein and thereto, without parting from thespirit and scope of the present invention.

What is claimed is:
 1. A method for simultaneously enhancing theproduction of both methane and volatile fatty acids in an anaerobicdigestion bioreactor, said method comprising: providing a stream oforganic feedstock; providing a plurality of anaerobic digesterbioreactors, each of said plurality of anaerobic digester bioreactorsconnected in series; step-feeding predetermined percentages of saidstream of organic feedstock to two or more of said plurality ofanaerobic digester bioreactors connected in series; feeding effluentfrom each of said plurality of anaerobic digester bioreactors to asubsequent one of said plurality of anaerobic digester bioreactors insaid connected series of anaerobic digester bioreactors; andanaerobically digesting at least one of said stream of organic feedstockand said effluent from each of said plurality of anaerobic digesterbioreactors to develop a final effluent stream including methane andvolatile fatty acids.
 2. The method according to claim 1, wherein saidplurality of anaerobic digester bioreactors includes six bioreactors. 3.The method according to claim 2, wherein at least one of said pluralityof anaerobic digester bioreactors is fed about 50 to about 80 percent ofsaid stream of organic feedstock and at least two of said plurality ofanaerobic digester bioreactors are each fed about 5 to about 15 percentof said stream of organic feedstock.
 4. The method according to claim 1,wherein one of said plurality of anaerobic digester bioreactors is fedabout 70 percent of said stream of organic feedstock and three of saidplurality of anaerobic digester bioreactors are each fed about 10percent of said stream of organic feedstock.
 5. The method according toclaim 1, wherein said organic feedstock includes one or more ofwastewater, sewage sludge, fecal sludge, agricultural waste, animalprocessing waste, municipal solid organic waste, food waste, andindustrial waste.
 6. The method according to claim 1, wherein an initialnitrogen concentration in said final effluent stream is about 4 to about10 percent of an initial volatile fatty acid concentration in saidstream of organic feedstock.
 7. The method according to claim 1, whereina temperature in each of said plurality of anaerobic digesterbioreactors is maintained at about 20 to about 40 degrees Celsius. 8.The method according to claim 1, wherein a pH in each of said pluralityof anaerobic digester bioreactors is maintained at about 5.5 to about7.0.
 9. The method according to claim 1, further comprising sterilizingvolatile fatty acids in said final effluent stream to an aerobic reactorusing a 0.2 pm filter.
 10. The method according to claim 1, furthercomprising: microbially converting volatile fatty acids in said finaleffluent stream to lipids.
 11. The method according to claim 10, whereinorganisms including a Cryptococcus albidus yeast, a Fusarium oxysporumfungus, or a combination thereof, microbially convert volatile fattyacids in said final effluent stream to lipids.
 12. A system forconverting volatile fatty acids to lipids, said system comprising: asupply stream of organic feedstock; a feedstock treatment module forproducing both methane and volatile fatty acids from said supply streamof organic feedstock, said feedstock treatment module including aplurality of anaerobic digester bioreactors fluidly connected in seriesand fluidly joined with said supply stream of organic feedstock and aplurality of adjustable valves for step-feeding predeterminedpercentages of said supply stream of organic feedstock to two or more ofsaid plurality of anaerobic digester bioreactors; and an aerobicbioreactor for converting said volatile fatty acids produced by saidplurality of anaerobic digester bioreactors in said feedstock treatmentmodule to lipids.
 13. The system according to claim 12, wherein saidplurality of anaerobic digester bioreactors includes six bioreactors.14. The system according to claim 13, wherein one of said plurality ofanaerobic digester bioreactors is step-fed about 50 to about 80 percentof said supply stream of organic feedstock and at least two of saidplurality of anaerobic digester bioreactors are each step-fed about 5 toabout 15 percent of said supply stream of organic feedstock.
 15. Thesystem according to claim 14, wherein one of said plurality of anaerobicdigester bioreactors is step-fed about 70 percent of said supply streamof organic feedstock and at least two of said plurality of anaerobicdigester bioreactors are each step-fed about 10 percent of said supplystream of organic feedstock.
 16. The system according to claim 12,further comprising: a feedstock pretreatment filter for sterilizingvolatile fatty acids in said supply stream of organic feedstock or in aneffluent of said plurality of anaerobic digester bioreactors.
 17. Thesystem according to claim 12, further comprising: a control module forautomatically monitoring operating conditions in said plurality ofanaerobic digester bioreactors including monitoring and controlling saidvalves, temperatures, and a pH.
 18. A method for simultaneouslyenhancing the production of both methane and volatile fatty acids in ananaerobic digestion bioreactor, said method comprising: providing astream of organic feedstock; splitting a first percentage of said streamof organic feedstock thereby developing a first split stream of organicfeedstock; feeding said first split stream of organic feedstock to afirst anaerobic digester bioreactor; anaerobically digesting said firstsplit stream of organic feedstock in said first anaerobic digesterbioreactor thereby producing a first anaerobic digester bioreactoreffluent including methane and volatile fatty acids; splitting a secondpercentage from said stream of organic feedstock thereby developing asecond split stream of organic feedstock; feeding said second splitstream of organic feedstock to a second anaerobic digester bioreactor;feeding said first anaerobic digester bioreactor effluent to said secondanaerobic digester bioreactor; anaerobically digesting said second splitstream of organic feedstock and said first anaerobic digester bioreactoreffluent in said second anaerobic digester bioreactor thereby producinga second anaerobic digester bioreactor effluent including methane andvolatile fatty acids; feeding said second anaerobic digester bioreactoreffluent to a third anaerobic digester bioreactor; anaerobicallydigesting said second anaerobic digester bioreactor effluent in saidthird anaerobic digester bioreactor thereby producing a third anaerobicdigester bioreactor effluent including methane and volatile fatty acids;splitting a third percentage of said stream of organic feedstock therebydeveloping a third split stream of organic feedstock; feeding said thirdsplit stream of organic feedstock to a fourth anaerobic digesterbioreactor; anaerobically digesting said third split stream of organicfeedstock and said third anaerobic digester bioreactor effluent in saidfourth anaerobic digester bioreactor thereby producing a fourthanaerobic digester bioreactor effluent including methane and volatilefatty acids; feeding said fourth anaerobic digester bioreactor effluentto a fifth anaerobic digester bioreactor; anaerobically digesting saidfourth anaerobic digester bioreactor effluent in said fifth anaerobicdigester bioreactor thereby producing a fifth anaerobic digesterbioreactor effluent including methane and volatile fatty acids; feedinga remaining percentage of said stream of organic feedstock to a sixthanaerobic digester bioreactor; feeding said fifth anaerobic digesterbioreactor effluent to said sixth anaerobic digester bioreactor; andanaerobically digesting said remaining percentage of said stream oforganic feedstock and said fifth anaerobic digester bioreactor effluentin said sixth anaerobic digester bioreactor thereby producing a finalanaerobic digester bioreactor effluent including methane and volatilefatty acids.
 19. The method according to claim 18, wherein said firstpercentage is about 50 to about 80 and said second, third, and remainingpercentages are each about 5 to about
 15. 20. The method according toclaim 18, wherein said first percentage is about 70 and said second,third, and remaining percentages are each about 10.